1. Field of the Invention
The present invention relates to a water heater, and more particularly to a water heater of the combustion type in which a heat exchanger is heated by a burner.
2. Description of the Prior Art
When it is attempted to improve the thermal efficiency of a water heater with use of a main heat exchanger having an increased area of heat transfer per unit output or an additional heat exchanger of the waste heat recovery type, the water vapor resulting from combustion condenses on the main or additional heat exchanger to produce a large amount of drain water during the use of the water heater. Since the drain water has dissolved therein SO.sub.x, NO.sub.x, etc. contained in the combustion gas, the water has a high acidity of about 2 to about 5 in pH and is therefore liable to cause corrosion to the burner and neighboring members. To overcome this drawback, heat exchangers for conventional water heaters are designed to have such a capacity that the exchanger will not release highly acidic drain water or will produce only a very small amount of drain water. Use of such heat exchangers entails the drawback of low thermal efficiency.